| Shizishan lead-znic deposit in Leichi was located,Leibo,Liangshan ofSichuanprovince, which40kilometers (linear distance) away from the Leibo countytown245°direction, the center for geographic coordinates is E:103°15′42″and27°54′38″. Shizishan lead-znic deposit located in the Yangtze continental block in thestructure of earth area in southwestern Paleozoic carbonate tableland of north westernedge，By holding in between Xiaojiang fracture and Huili-Ningnan-Jinyangfracture.The outcropping strata and the principal lithologic of the Shizishan mining areaare the gray-pale yellow tiger stripes limestone clip shale in the middle OrdovicianQiaojia group（O2q）, grey-dark grey marl, shale in the upper Ordovician Wufeng andQiancaogou group（O3）; the gray-pale yellow (calcium) shale, siltstone in the lowerSilurian Longmaxi group(S1l), the gray bioclastic limestone, dolomitic limestone inthe middle Silurian Daguan group(S2d); the gray shale, bauxite in the lower PermianLiangshan group(P1l), the gray bioclastic limestone clip dolomite in the lowerPermian Qixia group(P1q).Mine is located in the southern of Wanijiao anticlineplunging end and held in between NNE Luojie fracture and Jinyang-Quanshuijin-fracture. In the northern and southern mines were developed with twogentle anticline,it’s fold axis is the North West and North East respectively, in thecentral mines were developed with two normal faults (F1, F2) with80~128m lengthand1~2m width, both near the north-south direction.At present, it has been found that the3Pb-Zn ore-bodies in Shizishan deposit(No., ē, ē) are all produced in the middle Silurian Daguan group (S2d) whichinclude gray-thick layer of micro-fine grain bioclastic limestone and dolomiticlimestone. The occurrence of ore body and wall rock are basically the same, and theyare structure controlled by bedding slip zone and fracture zone. Spatial distribution ofore body is more stable, mainly is stratoid, lenticular, lenticular, veinlike, and localbranching, compound, dilation, apex shrinkage.Metal minerals include galena, pyrite, sphalerite, chalcopyrite, tetrahedrite,pyrrhotite; gangue minerals include calcite, dolomite, quartz, chlorite, sericite;oxidation minerals include cerussite, lead, vanadium ore, azurite, limonite, etc. Ore texture mainly has hypidiomorphic and xenomorphic granular structure, inlaid edgestructure, insert structure, metasomatic relict structure; ore structure includes themassive, vein, net veined, star point, disseminated, brecciated structure. The miningelement of the deposit is Pb, and they mainly galena. The wall rock alteration aremainly dolomitization, calcitization, silicification, pyritization etc. Ore deposits(bodies) have gone through the formation of sedimentary diagenetic period,hydrothermal mineralization period, surface oxidation mineralization stages.From the stratigraphic and lithologic combination, it follows that ore source layeris lower Cambrian Longwangmiao group（1l）, middle Cambrian Xiwangmiao group（2x）and middle silurian Daguan group (S2d). The former two groups containgypsum layer provided metallogenic mass SO42-, and abundant pb background andorganic carbon content which provide a large number of native Pb and H2S. Shieldinglayer is the lower Permian Liangshan formation (P1l), which is characteristics of theshale, clay rocks mainly plastic lithology. This layer has the blocking effects that iteffective prevented ore bearing hydrothermal migrating up. The middle SilurianDaguan group (S2d) is the host strata for the ore bodies. It developed several slidingzones and fault zones. These tectonic metallogenic provides favorable space for theore-forming. The silicification and carbonation altered the host strata, which increasedthe porosity and permeability of limestone, dolomite, that conducive to the infiltrationof the ore-forming elements and enrichment. The closed layer of lower SilurianLongmaxi group (S1l) contain mainly shale rock, whose structure is more compact,the permeability and chemical activity is low, so this group can effectively prevent theore bearing hydrothermal fluid infiltration.From the lithofacies palaeogeography perspective, during Early SilurianLongmaxi stage, mine is located in limited deep shelf environment, which formed alarge area of a thick layer of black shale, and a preliminary enrichment for variousmineral elements. While in Silurian Daguan period, further lift with regional groundup, the mining area started to shallow shelf from the deep shelf. So the sedimentaryenvironment is a semi enclosed lagoon reduction environment. And the daguan groupis rich in organic matters; SO42-can be restore to H2S, H2S, Zn2+and Pb2+to form PbSand ZnS, which is beneficial to the formation of the Pb-Zn ore.From the structural point of view, the formation of the Shizishan Pb-Zn deposit isthe product of the long-term development of the regional tectonic evolution. It processexperienced Chengjiang movement period, the Caledonian movement period,Hercynian, Indosinian movement, Yanshan movement and Himalayan movement period. From the relationship between structure and metallogenesis,Huili-Ningnan-Jinyang fault is ore conducting structure; the secondary fracture of theHuili-Ningnan-Jinyang fault (Luojie and Jinyang-Quanshui fracture) and Wanijiaoanticline are host structures; the two NS-striking faults (F1, F2) in the middle ofmining area, the early formation of the bedding slip zones, the secondary anticline,rock fracture zones and rock joint are the ore-bearing structures.In this paper, based on summarizing and analyzing the former data, we combinedthese with regional geological background of the Shizishan, focusing on the Shizishanlead-znic deposit geological feature, the metallogenic geological conditions; weconcluded the metallogenic regularity of ore deposit and point out the prospectingcriteria, so as to clarify the prospecting direction. The main achievements are asfollows:Shizishan Pb-Zn deposit of Leichi is located on north western edge of Yangtzeblock, i.e. the southwest of Paleozoic carbonate platform. This deposit sandwichedbetween the Xiaojiang Fault and Huili-Ningnan-Jinyang fault, the tectonic evolutionexperienced the Chengjiang movement, Caledonian, Hercynian movement, Indosinianmovement, Yanshan movement and Himalayan movement. The forming of thisdeposit resulted from combination of the deep structure and crust structure.The shielding layer of the Shizishan Pb-Zn deposit (body) is lower PermianLiangshan group (P1l) gray sandstone and shale; source layer is lower CambrianLongwangmiao group（1l），middle Cambrian Xiwangmiao group （2x）limestone,powder sandstone with gypsum layer and middle silurian Daguan group (S2d)limestone, dolomitic dolomite; host layer is the middle Silurian Daguan group (S2d)which is gray and dark gray, thick bedded bioclastic micro-fine grain limestone,dolomitic limestone. The closed layer is lower Silurian Longmaxi formation (S1l) greyshale, calcareous shale. The above-mentioned four groups with differentcharacteristics, which is forming, transporting, storing and cover system.The source bed of the Shizishan Pb-Zn deposit (body) is shallow lagoonenvironment of semi closed.The conducting structure of Shizishan Pb-Zn deposit (body) is the NS-strikingHuili-Ningnan-Jinyang fault, the ore host structure are the NNE-striking Luojie andJinyang-Quanshuijing inverse faults, the ore-bearing structure are sliding zone,secondary anticline, secondary faults and rock broken zone and rock joint.The wall rock alteration in Shizishan lead-zinc mine area are silicification,dolomitization, calcitization, pyritization etc., and these wall rock alteration are well indicator for prospecting.Combined with geological data and metallogenic regularity of Shizishan Pb-Zndeposit, we delineate, ē two class C prospecting area. |
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